Manufacturing Process of Semi-oxidized Tea(Chinese&Oolong tea)
Do you know your daily oolong tea is called “semi-oxidized tea?” In fact, most of the Chinese teas are categorized as “semi-oxidized tea.” Let us take a closer look at “semi-oxidized tea” and its manufacturing process and methods.
Features of semi-oxidized tea process (Chinese tea process)
“Semi-oxidized tea” is a tea whose fermentation (oxidization) has been stopped halfway. Tea leaves originally contain oxidative enzymes. The enzymes start oxidative fermentation right after harvesting. Stopping fermentation (oxidization) by heating at a suitable timing lends a unique color and flavor to semi-oxidized tea.
Fermentation or oxidation?
In the world of tea, fermentation refers to oxidation by oxidative enzymes in the tea leaf, not microbial or bacterial fermentation as in miso and yogurt. Oxidation refers to the reaction of enzymes with oxygen to change the original ingredients. Some teas such as post-fermented tea utilize microbes for fermentation, but as a rule, fermentation in the tea industry means oxidization.
Different types of semi-oxidized tea
Semi-oxidized tea is classified according to the degree of oxidation as follows:
Types of semi-oxidized tea
· White tea (bai cha): bai mudan, baihao yinzhen, etc.
· Yellow tea (huang cha): mengding huangya, junshan yinzhen, etc.
· Blue tea (qing cha): oolong tea, tieguanyin tea, etc.
Different oxidization degrees
“White tea” is a tea made from very young downy leaves still covered by white hair. It is featured by the short oxidation process. In addition, it is the only semi-oxidized tea that skips the rolling process.
“Yellow tea” is a tea that has been slightly oxidized during the Aracha (crude tea) phase. It undergoes the oxidation process, “menhuang,” which utilizes the leaf’s heat and moisture after heating treatment.
“Blue tea” is a representative type of semi-oxidized tea. It is called “blue tea” from the appearance of oxidized leaves that have turned reddish-brown and unoxidized leaves that remain green mixed together. Oolong tea is also a type of “blue tea.”
From picking fresh leaves to shipment
Every tea manufacturing starts from tea leaf picking called “plucking.” In the case of Chinese tea, unlike Japanese tea, tea leaves with a wider opening are to be picked. The picked leaves undergo withering, oxidization, rolling, drying, etc. to become “Aracha” and go through the finishing process at a finishing factory to be shipped.
How to make Aracha
There are various steps according to the type of tea. For example, in the case of ordinary oolong tea, the manufacturing method consists of sun-withering (shaiqing), indoor-withering (liangqing), rotary oxidization (yaoqing), pan-roasting (shaqing), wrapping (bao rou), rolling, and drying in this order to become Aracha.
1. Sun-withering (shaiqing)
The leaves are sun-dried in fine weather to be withered. The withering tank’s hot wind is also used in case of bad weather, but sun-dried ones are graded better in general.
2. Indoor-withering (lianqing)
Sun-withering makes the leaf temperature higher. The leaves need to be spread and cooled down on the indoor shelf before going to the next process.
3. Rotary oxidization (yaoqing)
The leaves are rotated in a bamboo basket to damage the leaf edges. Enzymatic oxidization gets activated from the damaged parts. The edges turn reddish-brown, while the inside of the leaf remains green. Now the leaves are semi-oxidized.
4. Pan-roasting (shaqing)
Oxidization is stopped at a right moment by roasting the leaves in the pan. The mainstream is hand-roasting with a tilted pan, but machine-roasting is coming on the scene nowadays.
As with Japanese tea, the leaves are kneaded under pressure. The process evenly spreads the leaf moisture so that the leaf ingredients get easy to come out.
6. Wrapping (bao rou)
The tea leaves are wrapped in a cloth roughly about 20 by 20 inches and shaped by squeezing and narrowing down in a rolling way. This process and the following drying process are repeated about 20 times.
The tightened bundle gets loosened and dried to remove the leaf moisture. Drying should take place slowly so that the leaves will not revert to the original shape by rapid drying. Then, the leaves are kept in a hemp bag to be transported to a finishing factory.
The leaves become Aracha after drying, but the leaves at this phase are not enough to be a product. Aracha needs to undergo “finishing” at the end.
Aracha is slowly roasted for the final adjustment of the leaf moisture. Roasting to a preferred degree brings out a nice flavor.
This completes the oolong tea process.